sql-server - SQL select join 帮助

Question

我在为这种情况找出查询时遇到问题。我想在此查询中使用两个表，它们是这样的:

Units
  ID
  Other Data
People
  ID
  UnitID  <-- fk to Units
  Other Data

这就是我想要做的:
我想选择所有在 People 表中没有一行链接到它们的单位。我该怎么做？

Answer 1

SELECT Units.* FROM Units LEFT JOIN People ON People.UnitID = Units.ID WHERE People.ID IS NULL

或者替代地

SELECT Units.* FROM Units WHERE NOT EXISTS (SELECT 1 FROM People WHERE People.UnitID = Units.ID)

甚至

SELECT Units.* FROM Units WHERE Units.ID NOT IN (SELECT UnitID FROM People)